1. Field of the Invention
The present invention relates to a slim blower fan installed in a notebook PC or the like.
2. Description of the Related Art
Fans have been arranged inside cases of a variety of electronic devices and household electrical appliances. In the case of notebook PCs and tablet PCs, for example, electronic components, such as CPUs, installed inside cases thereof generate heat, and measures need to be taken against the heat inside the cases. One common measure against the heat is to install centrifugal fans inside the cases to discharge the heat out of the cases.
In recent years, the market has been demanding a reduction in the thickness of the notebook PCs, and there has accordingly been a demand for reductions in the size and thickness of devices installed inside the cases of the notebook PCs. There also has been a demand for a reduction in the thickness of centrifugal fans arranged inside the cases, necessitating a reduction in the axial dimension of blades. However, in the case of a centrifugal fan having blades with a small axial dimension, energy applied by the blades to an air during rotation is small, resulting in a small air volume.
One known method of increasing the air volume is to provide air inlets in both an upper surface and a lower surface of a fan casing of a centrifugal fan as disclosed in JP-A 2008-157216. In addition, it is necessary to increase the rotation speed of the centrifugal fan to increase the air volume.
An increase in the rotation speed of fans, including the centrifugal fans, leads to an increase in a peak value of vibration in each frequency, and then vibrations may exert harmful effects on electronic components. In particular, vibrations are a significant issue for precision machines such as PCs.
Use of a cooling fan including a dynamic pressure bearing as disclosed in JP-A 2006-57838 is considered as a method of reducing vibrations which accompany rotation of the fan. Transfer of vibrations which occur in a rotating body to a case can be reduced by adoption of a dynamic pressure bearing which uses a liquid lubricant, such as an oil, in a bearing portion, since a circumference of a shaft is held by the lubricating fluid. The dynamic pressure bearing as disclosed in JP-A 2006-57838 includes a thrust dynamic pressure bearing extending radially, and this thrust dynamic pressure bearing prevents an excessive lift of the rotating body.
In the case of a fan including the above-described dynamic pressure bearing, the diameter of a rotor cup is necessarily large because the thrust dynamic pressure bearing extending radially is included in the dynamic pressure bearing, and the radial dimension of each blade is decreased relative to the diameter of the rotor cup. That is, a centrifugal fan which adopts a fluid dynamic bearing in order to reduce vibrations which accompany high-speed rotation tends to have a small air volume. That is, in the case of the centrifugal fan which adopts the fluid dynamic bearing, an air volume characteristic and a vibration characteristic stand in a trade-off relationship.